Well to explain the theories on pre-clovis; they think that rather than everyone coming over an ice bridge by Alaska, we may have ended up with early Europeans through boats along the coastline.
Personally, I'm not sure why we should question the concept of pre-clovis, but Scientists are being finicky for no reason. They were digging below a clovis trench and found- quite far down mind you- arrowheads/tools.